1. Field of the Invention
This invention relates to ion vapour deposition (herein IVD) by sputtering and relates to a method of and apparatus for applying coatings by IVD by sputtering.
The invention relates further to the application of coatings to articles, in particular optical lenses, and also to other articles of a width to thickness aspect ratio similar to optical lenses. The invention has particular application to optical lenses of the type used in spectacle frames, and which mainly will be corrective lenses, but could be plain lenses and in the interests of clarity reference is made hereinafter only to lenses which unless the context otherwise demands, are to be understood as being spectacle lenses.
The lenses to which the invention applies may be of glass or plastics material.
2. Description of the Prior Art
The IVD sputtering process comprises the placement of an article to be coated in a chamber in which is provided a cathode target of the coating material. Negative electric bias is applied to the target, and the chamber is filled with an inert gas, such as argon. Ionisation of the gas takes place, and the gas positive ions bombard the target by virtue of being attracted thereto due to the negative electric bias on the target. Sputtering of the target takes place which is a phenomenon resulting in the release of atoms of the target material into the chamber atmosphere. These atoms are caused to impinge upon the surface of the article to be coated and may be induced to deposit on the article by virtue of an electric bias on the article or in the region of the chamber surrounding the article, and so a coating is built up. The most usual forms of sputtering apparatus (magnetrons) use magnetic fields in conjunction with the target material to enhance the sputtering process.
IVD processes are of course well established for many products, and are typically used for metallic products which require to be coated to a high degree of accuracy, and where the articles have to be used in controlled environments or in situations where the performance of the articles is critical. For example IVD coated articles such as screws, nuts and bolts may be used in the aircraft industry, in military applications, or in space vehicle applications. The prior devices use a target with one material attached to it. Therefore only one single material can be sputtered from the target.
The use of IVD for the coating of spectacle lenses is also known but the available machines for such coating require the careful monitoring by skilled personnel; they are not in common use and generally speaking an alternative process known as evaporation is used for coating the lenses. Coatings on spectacle lenses perform several functions. Firstly, a reflection control coating serves to allow as much light of wavelength in the visible range through the lens into the eye as possible, whilst reflecting as much light which is in the harmful wavelength region, such as UV light, from the eye as possible. Other IVD coatings serve to provide a hard protective surface to protect the lenses from scratching and the like.
Generally speaking, the equipment which is used for IVD coating of lenses is evaporation equipment and is large and expensive, and requires considerable investment on the part of a processor, and in commercial terms when a person orders a pair of spectacles from an optician, the optician submits the prescription to a lens manufacturer, but the lens manufacturer in turn will pass on the lenses to the IVD coating processor who will coat the lenses as required. Coating in the conventional machine can take as much as one hour.